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I've written a udev rule which is run each time my device is mounted/dismounted.

However, in which Linux (Debian) error log should I check when debugging such rules?

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You can change logging priority to "info" level or even "debug" by:

udevadm control --log-priority=info

Then you will see all logs in your system log.

When you are done, bring it to default "err". See in /etc/udev/udev.conf what is your default logging level.

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I am confused why there are two points of configuration for logging priority. Care to explain how udevadm control --log-priority=info is different from setting udev_log="err" in /etc/udev/udev.conf? Thanks – silvernightstar Aug 29 '15 at 10:16
The udevadmmethod is to change the logging priority of the running udevd; udev.conf is for permanently changing it. – boycy Sep 6 '15 at 15:25

unbuffer udevadm monitor --environment The use of unbuffer is optional, but when piping output to grep saves you a headache. By default output is buffered in 4k blocks, nothing will be printed until that buffer is full.

You didn't forget to reload the rules? sudo udevadm control --reload

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Should be noted that unbuffer is not installed by default on Debian. – enzotib Apr 11 '12 at 19:14
That's correct, it is in the expect-dev package. It can be installed by sudo apt-get install expect-dev un Debian/Ubuntu. – jippie Apr 11 '12 at 19:21

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